Throughout this application various publications are referred to by number in parentheses. Full citations for these references may be found at the end of the specification. The disclosures of these publications, and all patents, patent application publications and books referred to herein, are hereby incorporated by reference in their entirety into the subject application to more fully describe the art to which the subject invention pertains.
Apoptosis plays a critical role in maintaining normal tissue homoeostasis in multicellular organisms and its deregulation results in an imbalance of homeostasis contributing to several diseases (1,2) The BCL-2 protein family plays a central role in regulating the mitochondrial pathway of apoptosis (3,4) The mitochondrial outer membrane permeabilization (MOMP) is considered the key event that is regulated by the complex network of protein-protein interactions between pro-apoptotic and anti-apoptotic members of the BCL-2 family. Activation of pro-apoptotic members BAX and/or BAK is required for induction of MOMP, whereas the anti-apoptotic or survival proteins such as BCL-2, BCL-XL and MCL-1, inhibit the pro-apoptotic proteins and prevent MOMP. Activation of BAX and BAK or inhibition of anti-apoptotic BCL-2 proteins is regulated by direct interaction with the BH3-only proteins.
The activation pathway of BAX represents the gateway to apoptosis and understanding the function of BAX and its regulation mechanisms is an area of intensive investigation. BAX is predominantly found in the cytosolic compartment in an inactive conformation (5,6). Upon cellular stress, BAX is triggered and undergoes a series of conformational changes that enable its translocation to the mitochondrial membrane and oligomerization leading to MOMP induction (7,8). The structure of the BAX monomer in the inactive conformation was previously determined by nuclear magnetic resonance (NMR) spectroscopy (9). The inactive BAX structure adopts a typical BCL-2 fold, consisting of nine α-helices linked with variable loops. In contrast to BAK and anti-apoptotic BCL-2 proteins that reside at the mitochondrial outer membrane, the structure of BAX was determined with its hydrophobic C-terminal helix α9 bound to the canonical hydrophobic groove. When the C-terminal α9 helix dissociates from the canonical hydrophobic groove, it binds to the mitochondrial outer membrane facilitating the mitochondrial translocation of BAX (9). Structural analysis of a hydrocarbon stapled BIM BH3 helix bound to monomeric BAX uncovered an activation site at the N-terminal surface of BAX (10). This activation site regulates the trigger mechanism for conformational activation of cytosolic BAX leading to the release of the hydrophobic α9 helix and exposure of the hydrophobic α2 helix (BH3 domain) (10-12). Mitochondrial translocated BAX undergoes further conformational changes on the membrane that induce BAX oligomerization and MOMP (13-16), or is inhibited by anti-apoptotic Bcl-2 proteins (17-20).
A number of diseases and disorder are associated with premature or unwanted cell death and characterized by abnormal activation of BAX. The present invention addresses the need for inhibitors of BAX activation for therapeutic treatments.